[PATCH net-next v3 1/5] net: Introduce NETIF_F_GRO_HW.

[Michael Chan <michael.chan@broadcom.com>]

Introduce NETIF_F_GRO_HW feature flag for NICs that support hardware
GRO.  With this flag, we can now independently turn on or off hardware
GRO when GRO is on.  Previously, drivers were using NETIF_F_GRO to
control hardware GRO and so it cannot be independently turned on or
off without affecting GRO.

Hardware GRO (just like GRO) guarantees that packets can be re-segmented
by TSO/GSO to reconstruct the original packet stream.  It is a subset of
NETIF_F_GRO and depends on it, as well as NETIF_F_RXCSUM.

Since NETIF_F_GRO is not propagated between upper and lower devices,
NETIF_F_GRO_HW should follow suit since it is a subset of GRO.  In other
words, a lower device can independent have GRO/GRO_HW enabled or disabled
and no feature propagation is required.  This will preserve the current
GRO behavior.

Cc: Ariel Elior <Ariel.Elior@cavium.com>
Cc: everest-linux-l2@cavium.com
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
---
 Documentation/networking/netdev-features.txt |  8 ++++++++
 include/linux/netdev_features.h              |  3 +++
 net/core/dev.c                               | 12 ++++++++++++
 net/core/ethtool.c                           |  1 +
 4 files changed, 24 insertions(+)

diff --git a/Documentation/networking/netdev-features.txt b/Documentation/networking/netdev-features.txt
index 7413eb0..8f36527 100644
--- a/Documentation/networking/netdev-features.txt
+++ b/Documentation/networking/netdev-features.txt
@@ -163,3 +163,11 @@ This requests that the NIC receive all possible frames, including errored
 frames (such as bad FCS, etc).  This can be helpful when sniffing a link with
 bad packets on it.  Some NICs may receive more packets if also put into normal
 PROMISC mode.
+
+*  rx-gro-hw
+
+This requests that the NIC enables Hardware GRO (generic receive offload).
+Hardware GRO is basically the exact reverse of TSO, and is generally
+stricter than Hardware LRO.  A packet stream merged by Hardware GRO must
+be re-segmentable by GSO or TSO back to the exact original packet stream.
+Hardware GRO is dependent on GRO and RXCSUM.
diff --git a/include/linux/netdev_features.h b/include/linux/netdev_features.h
index b1b0ca7..db84c51 100644
--- a/include/linux/netdev_features.h
+++ b/include/linux/netdev_features.h
@@ -78,6 +78,8 @@ enum {
 	NETIF_F_HW_ESP_TX_CSUM_BIT,	/* ESP with TX checksum offload */
 	NETIF_F_RX_UDP_TUNNEL_PORT_BIT, /* Offload of RX port for UDP tunnels */
 
+	NETIF_F_GRO_HW_BIT,		/* Hardware Generic receive offload */
+
 	/*
 	 * Add your fresh new feature above and remember to update
 	 * netdev_features_strings[] in net/core/ethtool.c and maybe
@@ -97,6 +99,7 @@ enum {
 #define NETIF_F_FRAGLIST	__NETIF_F(FRAGLIST)
 #define NETIF_F_FSO		__NETIF_F(FSO)
 #define NETIF_F_GRO		__NETIF_F(GRO)
+#define NETIF_F_GRO_HW		__NETIF_F(GRO_HW)
 #define NETIF_F_GSO		__NETIF_F(GSO)
 #define NETIF_F_GSO_ROBUST	__NETIF_F(GSO_ROBUST)
 #define NETIF_F_HIGHDMA		__NETIF_F(HIGHDMA)
diff --git a/net/core/dev.c b/net/core/dev.c
index e32cf5c..6ebd0e7 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -7424,6 +7424,18 @@ static netdev_features_t netdev_fix_features(struct net_device *dev,
 		features &= ~dev->gso_partial_features;
 	}
 
+	if (features & NETIF_F_GRO_HW) {
+		/* Hardware GRO depends on GRO and RXCSUM. */
+		if (!(features & NETIF_F_GRO)) {
+			netdev_dbg(dev, "Dropping NETIF_F_GSO_HW since no GRO feature.\n");
+			features &= ~NETIF_F_GRO_HW;
+		}
+		if (!(features & NETIF_F_RXCSUM)) {
+			netdev_dbg(dev, "Dropping NETIF_F_GSO_HW since no RXCSUM feature.\n");
+			features &= ~NETIF_F_GRO_HW;
+		}
+	}
+
 	return features;
 }
 
diff --git a/net/core/ethtool.c b/net/core/ethtool.c
index f8fcf45..50a7920 100644
--- a/net/core/ethtool.c
+++ b/net/core/ethtool.c
@@ -73,6 +73,7 @@ int ethtool_op_get_ts_info(struct net_device *dev, struct ethtool_ts_info *info)
 	[NETIF_F_LLTX_BIT] =             "tx-lockless",
 	[NETIF_F_NETNS_LOCAL_BIT] =      "netns-local",
 	[NETIF_F_GRO_BIT] =              "rx-gro",
+	[NETIF_F_GRO_HW_BIT] =           "rx-gro-hw",
 	[NETIF_F_LRO_BIT] =              "rx-lro",
 
 	[NETIF_F_TSO_BIT] =              "tx-tcp-segmentation",
-- 
1.8.3.1